How to Make a Cell Phone RF Signal Detector Circuit

A simple electronic circuit project is discussed here that may be built by any school student for displaying in a school fair science exhibition. The proposed circuit is a high gain opamp amplifier which detects slightest of RF disturbance that might be created by various electrical systems. Cell phone being the major generator of RF interference

is easily picked up by this circuit and can be seen through an LED illumination at the output of the circuit. The circuit is basically a simple high gain non inverting AC amplifier, built around the IC LM 324. Only two of its op amps may be incorporated, however for making the circuit extremely sensitive, all four of its opamps have been rigged in series. As mentioned in the earlier part of this article, the opamp is configured as a high gain non inverting amplifier, where the input is received at the pin #2which is the inverting input of the op amp. The RF disturbances in the air is received by the antenna and fed to the non inverting input of the opamp which is simply amplified by the circuit to some specified level depending on the value of the feed back resistor across the output and the non inverting input of the opamp. Increasing the value of this resistor increases the sensitivity of the circuit, however too much sensitivity can make the circuit unstable and induce oscillations. Here the relatively weaker signals from the first stage is further enhanced and made stronger so that now it may be fed to the third stage for repeating the actions that is for further amplification until the last stage whose output illuminate an LED, displaying the presence of even the minutest possible RF disturbance in the air. The discussed circuit of cell phone RF signal detector, sensor is very easy to build and requires minimal...